Alkene Reactions, Alkene Addition Reactions, Alkene Reactions (Orgo Chps. 7 & 8), Ochem Alkene Addition Reagents, Alkene practice, alkene/alkynes, Alkene Additions, Reactive Intermediates, Organic Chemistry 1- CH8- Alkene Reactions, Alkene Reactions,...
Hammond's postulate
"For an endothermic reaction, the structure and energy of the transition state resembles the structure and energy of the product"
DMS- Dimethylsulfate
((CH3)2S)
Hydrohalogen
(1)an alkene p system accepts a proton (H+) from an acid (HX) [the acid transfers a proton to the alkene], generating a carbocation; (2) the halogen anion combines with the carbocation.
Cleavage of 1,2 diols
(Its own category)
Dihydroxylation
(hydroxylation) the addition of two hydroxyl groups, one at each carbon of the double bond; formally, an oxidation
Allylic System Resonance (2) *
(write down)
Benzylic System Resonance (4) *
(write down)
[Hot alkaline] Potassium Permanganate Oxidation
*Gives cleaved alkene using KMnO4/H+ or KMnO4/Δ to get a ketone/aldehyde
Ozonolysis
*Gives cleaved alkene using O3/DMS to get a ketone/aldehyde 1. O3 reacts with alkene - forms cyclopentane 1a. Cyclopentane breaks to form two C=O bonds ([C=O(+)-O(-)] and [C=O]) 1c. Cyclopentane reforms and gives a free O and the two carbonyl groups 2. Addition of DMS: O attaches to S (DMS has resonance)
Simmons-Smith Reaction
*Gives unsubstituted cyclopropanes 1. ch2I2 and Zn(Cu) becomes CH2I and ZnI to attack double bond 2. Form [cis] cyclopropane
Diazomethane
*Wolff Rearrangement? *Carboxyl reacts with CH2N2 to make methyl ether 1. H in carboxyl group is lost to C anion in CH2N2 2. O anion in carboxyl reacts with CH3 and CH3-N2 bond is lost to N --> gives methyl ether
Hydrogenation
*alkene to alkane via syn addition H2/catalyst (Pd/C) or (Pt)
Halohydrins From Alkenes
-Addition of HX -Another example of an electrophilic addition is the reaction of alkenes with hypohalous acids (HO-Cl or HO-Br) to yield 1,2 haloalcohols called _________ -Previously saw when Br₂ reacts with an alkene the cyclic bromonium ion intermediate (R₂Br+) reacts with the only nucleophile present, Br- ion •but, if the reaction is carried out in the presence of an additional nucleophile, the intermediate bromonium ion can be intercepted by the added nucleophile and diverted to a different product •In the presence of a high [water], water competes with Br- ions as a nucleophile and reacts with the bromonium ion intermediate to yield a bromohydrin
Hydration of Alkenes: Addition of H₂O by Oxymercuration
-Addition of H₂O by _____ -Water adds to alkene to yield alcohols through a process called ___ -Reaction occurs by treating the alkene with water and a strong acid catalyst (H₂SO₄) by mechanism similar to that of HX addition •Protonation of an alkene double bond yields a carbocation intermediate, which reacts with water to yield a protonated alcohol product ROH₂+ --Loss of H+ from protonated alcohol gives the neutral alcohol and regenerates the acid catalyst -In the lab, alkenes are often ____ by the oxymercuration-demurcuration procedure ---Oxymercuration: electrophilic addition of Hg2+ to the alkene on reaction with mercury (II) acetate (Hg(CH₃CO₂)₂) in aqueous tetrahydrofuran solvent ---Intermediate organomercury compound then treated with NaBH₄ and demurcuration occurs to produce an alcohol -Regiochemistry of the reaction corresponds to Markovnikov addition of water: •OH group attaches to the more highly substituted carbon atom •the H atom attaches to the less highly substituted carbon -The H that replaces mercury in the demercuration step can attach from either side of the molecule, depending on the exact circumstances
Hydroboration-Oxidation
-BH3 -H2O2, NaOH Adds OH anti markov syn addition
Oxymercuration-Reduction
-Hg(OAc)2, H2O -NaBH4 Followed by reduction Converts alkenes to alcohols markov (adds OH)
Hydration of Alkenes: Addition of H₂O by Hydroboration
-In addition to the oxymercuration-demurcuration method (yields Markovinkov product), a complementary method, _____ , is also useful -yields anti-Markovinkov product -______: reaction involves addition of a B-H bond of Borane (BH₃) to an alkene to yield organoborane intermediate (RBH₂) ---Oxidation of the organoborane by reaction of basic hydrogen peroxide (H₂O₂) then gives an alcohol -Borane is very reactive as a Lewis acid because the boron atom has only 6 electrons in its valence shell; In tetrahydrofuran solution, BH3 accepts an electron pair from a solvent molecule in a Lewis acid-base reaction to complete its octet and form a stable BH3-THF complex
Halohydrin From Alkene Mechanism
-Mechanism: product formed by reaction of alkene with X₂ in the presence of water (acts as a nucleophile) to react with intermediate R₂B+/R₂Cl+ ion instead of Br-/Cl- 1.) reaction of alkene with X₂ yields a bromonium/chloronium ion intermediate 2.) water acts as a nucleophile using a lone pair of electrons to open the bromonium/chloronium ion ring and form a bond to carbon; since oxygen donates its electrons, it now has a (+) charge 3.) Loss of a proton (H+) from oxygen then give H3O+ and the neutral bromohydrin/chlorohydrin addition product -few alkenes are soluble in water and bromohydrin formation is often carried out in a solvent such as aqueous dimethylsulfoxide (CH₃SOCH₃) using reagent N-bromosuccinimide (stable easily handled and slowly decomposes in water to yield Br₂ at a controlled rate) as a source of Br₂ -formation, like halogenation, is carried out by haloperoxidases in biology
Halohydrin Formation
-Solvent does not act as nucleophile -Solvent is H2O -ends with a halogen substituent and OH substituent -X2 and H2O Markov w/OH anti-addition
Halogenation of Alkenes
-addition of X₂ -Br₂ and Cl₂ add rapidly to alkenes to yield 1,2-dihalides through _______ -When performed on a cycloalkene only trans stereoisomer is formed rather than the mix of the cis/trans isomers expected if a planar carbocation intermediate were involved -Reaction occurs with stereochemistry (two halide atoms come from opposite faces of the double bond--one from the top and one from the bottom) -Reaction intermediate is not a carbocation but instead is a bromonium/chloronium ion (R₂B+ or R₂Cl+) by electrophilic addition of Br+/Cl+ to the alkene •formed in a single step by interaction of the alkene with Br₂+ and simultaneous loss of Br- -Primarily limited to marine organisms living in halide-rich environments •carried out by haloperoxidases (use H₂O₂ to oxidize Br- and Cl- ions to a bio equivalent of Br+ or Cl+) •yields a bromonium or chloronium ion intermediate just as in the lab and reaction with another halide completes the process
Halogenation
-adds X2 -only done for Cl2 and Br2 -F2 is too violent (many side products) -I2 undergoes addition but has very unstable product -solvent is CHCl3 -Anti addition -stepwise addition -no carbocation
stereoselective (in comparison to stereospecific)
-one stereoisomer formed more than others -rxn has a choice of pathways but one is preferred over the other
stereospecific
-stereochemistry of starting material determines stereochemistry of product -no choice involved
Hydrogenation
-typically H2 and Pt -gets rid of double bonds -Arene ring will be unchanged syn addition
Radical molecule reaction types
1. Abstraction (transfer) 2. addition to multiple bonds (produce radicals)
Hydroboration/Oxidation
1. BH3 (H-BH2) + THF / 2. H2O2 + NaOH *BH2 on LEAST substituted C of double bond *H2O2 replaces BH2 with OH (or simply just place OH on least substituted C)
Dichlorocarbene
1. Base (-O of NaOH) attacks H in chloroform to make H2O 2. C(Cl)3 loses a Cl to make a carbene 2. Carbene reacts w alkene to make dichlorocarbene cyclopropane
Radical-radical reaction types
1. Combination 2. Disproportionation
Radicals may be stabilized by:
1. Delocalisation 2. Adjacent groups (captodative effect) 3. Steric effects
Unimolecular radical reaction types
1. Fragmentation (ß-scission) 2. Rearrangement
hydrogenation/reduction (alkyne)
1. H2, Pd/C = alkane 2. H2, Lindlar's cat = cis alkene 3. Li, NH3 = trans alkene
Acid-Catalyst and Water
1. H3O attack on double bond (OH on more subt.) 2. H2O attack on carbocation, H2O attack on H2O to form OH and H3O+
Oxymercuration/Demercuration
1. Hg(OAc)2 followed by 2. NaBH4 *attack on double bond --> Mercurmium Ion Interm. *H2O attacks more substituted carbon (lose an H) *NaBH4 replaces Hg(OAc)2 with H
Nitrene reaction types
1. Insertion into CH bond 2. cycloaddition to alkenes and arenes 3. Hofmann Rearrangement (amide -> amine with loss of C)
Dihydroxylation
1. OsO4 attacks double bond to form cyclic, osmate ester 2. H2O2 attacks O-C bonds to form two syn/cis diols
Electron transfer reaction types
1. Oxidation 2. Reduction
Radical carbon to carbon bond formation types
1. Pinacol reaction (2 ketones -> diol) 2. addition to an unsaturated compound 3. intramolecular reactions
Radical Generation Types
1. Thermal cleavage of bonds 2. Photochemical cleavage of bonds 3. Electron transfer reactions (redox)
Alternatives to tributyltinhydride
1. Tributyl germanium hydride Bu3GeH - non-toxic and easier to remove -> not very stable so has to be made immediately before use from GeCl4 (expensive) and Bu3MgBr. 2. Tristrimethylsilyl silane (Me3Si)3SiH - non-toxic and easy to remove -> used under argon and is expensive. Also has a tendency for the (Me3Si)3Si radical to add directly to double bonds
Halogenation
1. X-X attack double bond to form cyclopropane intermediate 2. Add X ion to form trans-vicinal or anti-
Halohydrin Formation (Hypohalous acids)
1. X-X attack on double bond 2. H2O attack (twice) to form trans/anti *If alkene is NOT symmetrical, -OH is on the MORE substituted C. IF symmertrical, doesn't matter.
Autoxidation reaction examples
1. alkylarenes 2. ethers
bromination of (R)-4-tert-butylcyclohexene
1. bromine atoms must add in an axial manner, each bromonium ion intermediate reacts with bromide ion to give the same product. 2.the presence of the bulky tert-butyl group controls the orientation of the two bromine atoms adds to the ring.
Arynes - generation types
1. from aryl anions 2. from zwitterions 3. from aryl triflates
Nitrenes - generation types
1. from azides (contain N+=N-=N) 2. By α elimination reactions (base needed)
Arynes - reaction types
1. nucleophilic addition 2. 2,4-addition to 1,3-dienes 3. 2,2-addition to alkenes
Radicals - types of reaction
1. radical radical reactions 2. radical molecule reactions 3. Unimolecular radical reactions 4. Electron transfer reactions
Features of electrophiles
1. region of low electron density 2. lack of octet 3. relatively weak bond to atom that can make stable ion/molecule
Halohydrine(Br2/H2O)
1. trans-addition 2)it is limited to introducing the OH group at the more highly substituted carbon, according to Markovnikov; 3)carbocation rearrangements may interfere with or prevent the synthesis of a desired alcohol by that method
Disadvantages of tributyltinhydride
1. very difficult to remove tin residues after rxn is complete 2. tin v. toxic - so limited use in pharmaceutical synthesis
Oxymercuration
3 membered ring, markovnikov, syn and anti
Bromination
3-membered ring, N/A (regiochemistry), anti
Halohydrin formation
3-membered ring, markovnikov, anti
Chlorination
3-membered ring, n/a, anti
Hypohalous Acids via NBS/DMSO/Water *
?
Glycol
A compound with hydroxyl(-OH) groups on adjacent carbons.
enantioselective
A reaction that produces one enantiomer in preference to the other.
stereospecific reaction
A special type of stereoselective reaction in which the stereochemistry of the product is dependent on the stereochemistry of the starting material.
Roles of ABCN and Bu3SnH in the reduction of alkyl halides
ABCN is the initiator, tributyltin hydride is the radical carrier
Radicals - intramolecular reactions - reaction conditions
AIBN and tributyltinhydride (small amount), Br-hydrocarbon turns into hydrocarbon radical, PhMe as solvent
Hydrohalogen#2(trans)
Above is a two-step reaction - the first step is regiorandom (because the carbons are equivalent); in the second step one stereocenter is generated. Because this step is stereorandom, a racemate is formed.
Hydrohalogen#3(no chiral center, trans alkene)
Above is a two-step reaction - the first step is regiospecific, generating the more stable carbocation; in the second step a new stereocenter is generated. However, the addition of Br- is stereorandom; therefore a racemate is formed.
Mark
Acid catalyze hydration
Hydrohalogenation
Acid catalyze hydration and ___ have carbocation intermediates
H2O, H2SO4
Acid-catalyzed hydration Markovnikov Carbocation rearrangements possible Alkene -> Add H, OH
catalytic hydrogenation
Adding H2 (g) across a carbon-carbon double bond in the presence of a transition metal catalyst Product: alkane
Acid Catalyzed Hydration
Adding OH to break the pi bond and hydrogen is put on the most and least substituted carbon while OH is added to the tertiary (?) carbon
Radical Polymerization
Addition Reaction
Carbenes
Addition Reaction 1. Dichlorocarbene Addition 2. Simmons-Smith Reaction
Addition of Halogens (Cl2 or Br2)
Addition Reaction Anti-addition observed through a *halonium* intermediate
Hydroxylation by acid catalyzed epoxide hydrolysis
Addition Reaction Anti-stereochemistry occurs
Addition of HCl or HBr
Addition Reaction Markovnikov
Halohydrin Formation
Addition Reaction Markovnikov Anti-stereochemistry
Catalytic Hydrogenation
Addition Reaction Syn addition occurs
Epoxidation with a peroxyacid
Addition Reaction Syn addition occurs
Hydroxylation with OsO4
Addition Reaction Syn addition occurs
Hydroboration/Oxidation
Addition Reaction The addition of water via this process Non-Markovnikov
Oxymercuration
Addition Reaction The addition of water via this process Markovnikov
Reactions with Carbocation Intermediates (2)
Addition of HX to an Alkene Addition of water and an acid catalyst (has rearrangement)
Markovnikov Alcohol
Addition of X to more substituted C and H to C with more H's (Regioselective) ; most likely major product
Acid Catalyzed Hydration
Addition of water across double bond, needs a strong acid catalyst, involved carbocation intermediates
X2/H2O
Adds 1 OH and 1 halogen, OH is markonikov, No carbocation intermediate
Acid Catalyzed Hydration features
Adds OH at more substituted carbon H2SO4 and H2O Carbocation intermediate markov addition
Halogenation
Adds halogens (Cl2 and Br2) No carbocation Adding 2 of the same halogen across the pi bond Anti addition and bridge intermediate Product= alkyl dihalide Ignore regiochemistry Can also give rise to meso compound if starting compound is symmetrical Arrow?
Reaction: Ozonolysis
Aldehyde
1) O3 2) Me2S
Aldehyde/Ketone
Reaction: Potassium Permanagante
Aldehydes are oxidized to Acids
42
Alkene pKa
1.Mg 2.Co2 3.HCL
Alkyl halide to carboxylic acid
Cl2, heat
Allylic halogenation Alkene -> Cl-C-C=C
Reaction: Addition of Halogens
Anti
Reaction: Anti Dihydroxylation
Anti
1) MCPBA (RCO3H) 2) H3O+
Anti Dihydroxylation Trans addition Epoxide intermediate Alkene -> Add OH, OH
Oxymercuration-Demercuration
Anti addition No carbocation H+ and OH across pi bond Form bridge intermediate Product= alcohol Regiospecific - only mark made Want reducing agent (NaBH4) Arrow?
1) RCO3H 2) H3O+
Anti addition adds OH to each double bonded C
X2
Anti addition adds halogen to each double bonded C
Reaction: Hydroboration-Oxidation
Anti-Markovnikov Syn
Hydroboration/Protonolysis*
Anti-Markovnikov Alc. 1.
HX ROOR
Anti-Markovnikov addition Mixed addition adds X to least substituted C
1) BH3 * THF or B2H6 2) H2O2, NaOH
Anti-Markovnikov addition Syn addition adds OH to least substituted C OH and H cis/syn
Halogen Addition/ Br2 Addition/ Bromination/ Alkene Addition (Br2)
Anti-addition halonium ion (bromonium ion) intermediate
Halohydrin (Bromohydrin) formation (Br2, H2O in excess)
Anti-addition substitution with inversion (OH adds on side opposite Br) OH adds on most substituted carbon, Br adds on least substituted halonium ion intermediate
halogenation (X2 w/ CCl4)
Anti-syn
Dihydroxylation (mcpba w/ H3O+)
Anti-syn addition
X2
Anti/trans "triangle" intermediate
π radical example
Benzyl (PhC•H2), PhO•, PhN•R, allyl
Radicals - addition to unsaturated compounds - reaction conditions
Best result if alkene has EWG substituent, AIBN and tributyltinhydride for initiation
Ozonanylsis
Break alkenes Every pi bond breaks to form double bonded oxygens (on both carbons) Get ketones, aldehydes, carboxcylic acids Reducing and oxidizing (more oxygens) Disub; monsub
Br2, CCl4
Bromination Anti addition Alkene -> Add Br, Br
Reduction of alkyl halides - initiation produces
Bu3Sn• radical
forms what in first step
C+ intermediate
Aldehyde
C=O and one alkyl group and an H
Ketone
C=O and two alkyl groups
Chloroform
CHCl3 -used in Dichlorocarbene rxn
Carbenes - structure and reactivity
Carbenes are neutral, electron deficient (6 e-) and highly reactive, with 2 non-bonded electrons. Most carbenes have triplet ground states as this is slightly lower in energy as both single electrons are in individual orbits. But if the adjacent atom has a lone pair then the ground state may be a singlet due to π donation. Electrophilic, since they are e- deficient.
Addition of HX
Carbocation, markovnikov, syn and anti
Hydration
Carbocation, markovnikov, syn and anti
Radical addition
Carbocation?, anti, syn+ anti
Creating Alcohols
Carbocations are reactive intermediates; they react with various nucleophiles, not just halide ions. H+ catalyzed addition of H2O leads to alcohols. (Use H2SO4 because - OSO3H is a poor Nu, doesn't add like Br-) The first step is equivalent to that of hydrohalogenation.
hyperconjugation
Carbocations of higher degree are more stable beacue of the ability of surrounding carbons to share electrons more effectively with the carbocation, and the effect of ______ (when an empty p-orbital can share e-s of antiperiplanar atoms).
sp2
Carbons in 1 double bond on an alkene are ___ hybridized.
sp3
Carbons with tetrahedral geometry are ___ hybridized.
stereospecific syn
Catalytic hydrogenation
Reaction: Olefin Metathesis
Cis and Trans
Ozonolysis
Cleavage with reductive or oxidative work ups
Ozonolysis (O3 w/ (CH3)2S) or (O3 w/ H2O2)
Cleaves pi-bond
1) O3 2) Me2S
Cleaves the C==C bond O== adds to each C in the original alkene
Hydrogenation
Concerted, N/a, syn
Hydroboration
Concerted, antimarkovnikov, syn addition
Dihydroxylation
Concerted, n/a, SYN
Cyclepropanation
Concerted, n/a, syn
Epoxidation
Concerted, n/a,syn
stereospecific syn
Dihydroxylation
Alkene + RCO3H
Direct epoxidation. draw RCO3H ring like with O-H towards alkene
Captodative effect
EWG/EDG may stabilise radical due to lower energy levels
halohydrin formation (X2 w/ H2O)
Enantiomers are present anti-markovnikov anti-syn NO CARBOCATION INTERMEDIATE!
atropisomers
Enantiomers that lack a chiral center and differ because of hindered rotation.
stereospecific syn
Epoxidation
Syn
Epoxidation addition
mCPBA
Epoxidation reagent
Alkene + C2H4O3 (peroxyacid)
Epoxide! ie O ring + CH3COOH
HBr with Peroxides
Favor non mark- least sub carbon Br is added to least substituted carbon Make tertiary radicals (stability) Make radical intermediate
X2, anti, neither
For a halogenation reaction, ____ is the reagent and the two atoms from that reagent add in a (syn/anti/either) addition. This product is (anti/not anti/neither) Markovnikov.
X2, H2O, anti, not anti
For a halohydration reaction, ____ & ___ are the reagents and the two groups from that reagent add in a (syn/anti/either) addition. This product is (anti/not anti/neither) Markovnikov.
HA, H2O, either, not anti
For an acid catalyzed hydration reaction, ____ & ___ are the reagents and the two groups from that reagent add in a (syn/anti/either) addition. This product is (anti/not anti/neither) Markovnikov.
H3C/Mgbr
Gringard reaction ketone or aldehyde to alcohol
Hydrohalogenation using the ROOR (peroxide or extreme heat or light)
H is added to the most substituted place and halogen is added to the least substituted place; not syn or anti
electrophile
H+ adds to sp2 C bonded to most H
Rank relative reactivity HCl HBr HI HF
HF < HCl < HBr < HI
Hydrohalogenation
Halogen to a hydrogen; Halogen is the most substituted while hydrogen is the least substituted; pi bond is broke; carbocations form so rearrangements happen (not syn or anti addition)
stereospecific. anti-addition because they add one at a time.
Halogenation
Anti
Halogenation addition
Anti
Halohydrin addition
Br2, H2O
Halohydrin formation Anti addition -OH more substituted Alkene -> Add Br, OH
Radicals formed when bond is broken...
Homolytically
Anti mark
Hydroboration
stereospecific syn
Hydroboration-oxidation
1) BH3, THF 2) H2O2, NaOH
Hydroboration-oxidation Anti-markovnikov Syn addition Alkene -> Add H, OH
Reactions that form Alcohols (4)
Hydroboration/Oxidation (anti-Markov. alc.) HBr and Peroxides (anti-Markov. alc.) Acid-Catalyst and water (Markov. alc.) Oxymercuration/Demercuration (Markov. alc.)
Reactions that require Stereochemistry (7) *
Hydroboration/Oxidation (cis/syn) Hydroboration/Protonolysis (syn) Halogens[X2] (trans- vicinal/anti) Hydrohydrin formation (trans/anti) Dihydroxylation (cis/syn) (Reverse) Epoxide (trans- dihydroxylation/anti) Hydrogenation (syn)
HBr, H2O2
Hydrobromination Anti-markovnikov Alkene -> Add H, Br
Syn
Hydrogenation
H2, Pt
Hydrogenation Syn addition Alkene -> Add H, H
HX
Hydrohalogenation Markovnikov Alkene -> Add H, X
Not stereospecific.
Hydrohalogenation AND Acid-catalyzed alkene hydration
halohydrin formation
If another nucleophile species (solvent) is present in the halogenation rxn, that nucleophiles can attack the cyclic halonium electrophile
How does the formation of a bromonium ion (R₂Br+) account for the observed anti-stereochemistry of addition to cyclopentene?
If bromonium ion is formed as a intermediate the large bromine atom might shield one side of the molecule; reaction with Br- ion in the 2nd step could then occur from the opposite unshielded side to give the trans product
Molozonide
In an ozonolysis reaction, an intermediate with molecular structure featuring a five-membered ring containing three adjacent oxygen atoms.
OH
In halohydrin formation, ___ is markonikov
Nitrenes must be generated...
In situ, since they are transient species.
Steric effects may...
Inhibit radical from reacting (stability: Isopropyl radical>>Methyl radical)
major
Is the product of this reaction the major or minor product?
minor
Is the product of this reaction the major or minor product?
CrO3, H2SO
Jones reagent turns primary alcohols into carboxylic acids, secondary into ketone
Reaction: Acid Catalyzed Hydration
Markovnikov
Reaction: Addition of Hydrogen Halides
Markovnikov
Reaction: Alkoxymercuration-Demercuration
Markovnikov
Reaction: Oxymercuration-Demercuration
Markovnikov
Acid Catalyzed Hydration (H2O, H3O+ or H2SO4)
Markovnikov carbocation intermediate rearrangements possible
Hydrogen Halide Addition (HBr)
Markovnikov carbocation intermediate rearrangements possible
Reaction: Halohydrin Formation
Markovnikov Anti
alkene + H2O/H2SO4
Markovnikov addition Mixed addition adds OH to most substituted C adds hydrogen to least substituted C
HX
Markovnikov addition Mixed addition adds halogen to most substituted C adds hydrogen to least substituted C
X2 H20
Markovnikov addition of OH Anti addition OH placed at most substituted C, X placed at least substituted C
Mark
Mercuration reduction
Oxymercuration
Mercury (Hg(OAC)2) added along with an H2O; also uses NABH4; adding H2o so HOH; adds OH on most substituted and puts hydrogen on the less substituted; markonikoiv; anti addition
ALkmercuration
Mercury (Hg(OAC)2) added along with an H2O; also uses NABH4; adding ROH so chain with OH; anti addition
Pinacol reaction - reaction conditions
Mg (to donate e-, and allow complexing), 80°C, benzene
1-bromo-butane
Name the product
butene
Name the reactant (all the way to the left)
Halohydrin Formation
No carbocation Halogen + OH = bridge intermediate Anti Addition Product = halide alcohol Regiospecific= one product- Mark OH on more substitued carbon Arrow?
Hydrogenation
No carbocation Product= alkane Add 2 H+ Syn addition Turn all alkenes to alkanes No regiochem Requires metal catalyst Arrow?
Epoxide Formation
No carbocation Product= epoxide Add Oxygen bridge No bridge intermediate Syn Addition No regiochemistry Does not change stereochemistry from alkene Either both cis/trans Arrow?
oximercuration/reduction
No rearrangements
Ozonolysis
O3 and SMe2 breaks double bonds
Vicinal
On adjacent carbons
(Reverse) Epoxide
Open an epoxide to get trans/anti-dihydroxylation 1. Add H3O+ to break cyclopropane bond 2. Add the H2O to the C that loses the bond after step 1 -Add H2O again to form OH from H2O attached -Anti-addition
dihydroxylation
OsO4 and tBuOOH adds 2 OH syn addition
Reaction with KMnO4 in acidic solution
Oxidative Cleavage of Alkenes
Reaction with ozone followed by zinc in acetic acid
Oxidative Cleavage of Alkenes Intermediates: [Molozonide] and Ozonide
Oxidative cleavage (KMnO4 w/ H3O+ or hot)
Oxidizes and cleaves
Mark
Oxymercuration
1) Hg(OAc)2, H2O 2) NaBH4
Oxymercuration-demercuration Markovnikov No carbocation rearrangements Alkene -> Add H, OH
anti-addition
Oxymercuration-reduction
Reactions that form Cyclopropane Intermediates (3)
Oxymercuration/Demercuration (mercurmium ion interm.) Halogenation (bromonium/chloroniumion interm.) Hydrohydrin Formation
1) O3 2) DMS
Ozonolysis Allene cleavage -> 2 C=O
Reaction: Polymerization
Polymer (lol)
Oxidative Cleavage
Puts an oxygen on either side of the break; can use KMNO3 & hot, can also use O3and H2O2 which forms an double bonded O from the double bond and with an OH
Autoxidation reaction (radical)
R3C-H + O2 ---> R3C-O-O-H (hydroperoxide) ---> alcohols, ketones, carboxylic acids formation of R-O-O• radical
Reduction of alkyl halides
RBr + Bu3SnH ---ABCN/∆---> RH + Bu3SnBr
nucleophile in addition of alcohol to alkene
ROH like CH3OH, adds to C+ forming a protanated ether
Hyrdohalogenation
Racemic Double bonds is nucleophile; H+ is electrophile Regioselect mark Form carbocation Arrow? Take H+ from less substituted carbon
Acid Catalyzed Hydration
Racemic Forms carbocation Regioselect mark Takes from acid - donates protons Addition of OH and the end Principle of Microsocpic Reversibility applies Arrow?
-2 chiral centers in products -Z and symmetric -no H's on Double Bond Br₂,H₂O
Racemic mix of R,R and S,S
Antimark
Radical hydrohaogenation
Why must the solvent be deoxygenated before use?
Radicals very reactive - no unwanted byproducts
LiAlH4
Reduces carboxylic acids and esters to alcohols
Halohydrin (X2 in water) (Mech type)
Regio: Markovnikov Stereo: Anti
HX addition to alkenes (Mech type)
Regio: Markovnikov Stereo: N/A
Oxymercuration-demercuration (Mech type)
Regio: Markovnikov Stereo: N/A
X2 in organic solvent (Mech type)
Regio: N/A Stereo: Anti
Ozonolysis (Mech type)
Regio: N/A Stereo: N/A Oxidative cleavage
Acid-catalyzed epoxide opening (Mech type)
Regio: N/A Stereo: anti
Catalytic hydrogenation (Mech type)
Regio: N/A Stereo: syn
Epoxidation (by peroxyacid) (Mech type)
Regio: N/A Stereo: syn
Osmylation (Mech type)
Regio: N/A Stereo: syn
Hydroboration (Mech type)
Regio: Non-Markovnikov Stereo: syn
H2/Pd
Removes double bond or triple bond
HX; ether Regio: Markovnikov Addn
Steps/reagents involved
Syn
Stereoselectivity w/ BH3
Both
Stereoselectivity w/ H-X
Anti
Stereoselectivity w/ HO-X
Anti
Stereoselectivity w/ Hg(OAc)2
Anti
Stereoselectivity w/ RS-Cl
Anti
Stereoselectivity w/ X2
NANH2
Strong base that is used for deportation of alkenes and elimination reactions (turns things into alkynes)
What affects reactivity of carbenes?
Substituents - EWGs makes carbenes more electrophilic EDG reduce electrophilicity and reactivity
Reaction: Alpha Elimination for Cyclopropanation
Syn
Reaction: Catalytic Hydrogenation
Syn
Reaction: Epoxidation
Syn
Reaction: Simmons Smith Cyclopropanation
Syn
Reaction: Syn Dihydroxylation
Syn
Hydroboration
Syn Addition No carbocation Regioselect non mark Only way to get primary OH group Adds H+ and OH across double bond Need H2O2 Arrow?
KMnO4, NaOH, cold
Syn Dihydroxylation Method 1 Alkene -> Add OH, OH
1) OsO4 2) H2O2
Syn Dihydroxylation Method 2 Alkene -> Add OH, OH
Syn Dihyroxylation
Syn addition 2 OHs = no regiochem Has the ability to make meso compounds Arrows (2 possible)?
H2 Pt (Pd/C)
Syn addition Removes the alkene with the addition of H to each double bonded C
1) OsO4 2) NaHSO3, H2O
Syn addition adds OH to each double bonded C
KMnO4 NaOH, cold
Syn addition adds OH to each double bonded C
Dihydroxylation (OsO4)
Syn addition diols (OsO4)
Dihydroxylation (KMnO4 w/ cold or base)
Syn addition diols! (KMnO4)
oxidation of alkenes by osmium tetroxide in the presence of peroxides
Syn hydroxylation of cis--butene gives meso-, -butanediol ; because the meso compound is achiral, the product is optically inactive. Syn hydroxylation of trans--butene gives racemic , -butanediol. Because the diol is formed as a racemic mixture, the product of the oxidation of the trans-alkene is also optically inactive. Thus, the osmium tetroxide oxidation of an alkene is stereospecific
Alkene halogenation
The addition of X2 (x=halogen) to alkenes, product is a vicinal dihalide
Stereochemistry of Halogenation(cis)
The bromonium ion formed from cis-butene is a meso species. Ring opening of a meso species by backside attack generates a racemic mixture.
Stereochemistry of Halogenation(trans)
The bromonium ion formed from trans-butene is a racemate. Ring opening by backside attack of a racemate generates a meso compound.
2, 3, carbon
The carbocation is rearranged from a ___ degree carbocation to a ___ degree carbocation by a 1,2-_____shift.
anti, either
The difference between the products of an oxymercuration demercuration reaction and a acid catalyzed hydration reaction is that oxymercuration demercuration produces (syn, anti, either) products, while acid catalyzed hydration produces (syn, anti, either) products.
Alkene halogenation regioselectivity
The nucleophile attacks the more substituted carbon first
solvent for Addition of Halogens to Alkenes
The reaction is commonly carried out in an inert solvent such as CH2Cl2, CHCl3, or CCl4.
HX
There are two reagent sets that can product hydrohalogenation. Which produces a markovnikov product?
HX, ROOR
There are two reagent sets that can product hydrohalogenation. Which produces an anti-markovnikov product?
Persistent Carbon Radicals may occur when...
There is enough stabilisation
Hygrohalogen#4(with one chiral center)
This is a two-step reaction - the first step is regiospecific, generating the more stable carbocation. In the second step a new stereocenter is generated; this is additional to the one alreadyexisting. Because this (second) step is stereorandom, a pair of diastereomers is formed.
Hygrohalogen#6(stereo select)
This is a two-step reaction - the second step is stereoselective, preferentially generating the anti- (or trans-) diastereomer. Reason: one methyl group hinders the approach of the nucleophile (Br-).
free radical substitution (bromination).
This method uses a series of repeating steps, which achieve the addition of H-Br in antiMarkovnikov fashion.
acid-catalyzed hydrohalogenation
This reaction is an example of ________.
X2 H2O
Trans/anti
Halohydrin Formation
Treatment of an alkene with chlorine (bromine) and water results in formation of a chlorohydrin (bromohydrin) having the halogen and hydroxyl groups on adjacent carbons. The mechanism involves nucleophilic attack of water on a bridged halonium ion. Net anti addition of the halogen and OH groups occurs. Consequently, product derived from a cycloalkene has the halogen and OH trans to each other.
Alkene + Br2/CCl4
Two bromines on neighboring C trans
Hydroboration
Uses BH3, THF & NAOH, H2O2 (sometimes H2O) is antimark so hydrogen adds to most substituted while oh adds to least; is syn addition
Dihydroxylation (Uses KMNO4 in cold conditions, dilute)
Uses KMNO4 in cold conditions, dilute
Hydrogenation
Using metals such as pt or pd along with H2; pi bond is broke and hydrogen atoms are added to each of the carbons; it is syn addition so both would be wedges or dashes
OH, H
What are the groups added in acid catalyzed hydration?
X, X
What are the groups added in halogenation?
OR, X
What are the groups added in halohydrin formation?
OH, H
What are the groups added in hydroboration oxidation?
H, X
What are the groups added in hydrohalogenation?
OH, OH
What are the groups added in hydroxylation?
OH, H
What are the groups added in oxymercuration demercuration?
1
What degree carbocation intermediate is formed?
2
What degree of carbocation intermediate is formed?
acid catalyzed hydration
What is the 4th blank from the top?
oxymercuration demercuration
What is the 5th blank from the top?
hydroboration oxidation
What is the 6th blank from the top?
hydroxylation
What is the 7th blank from the top?
hydrohalogenation
What is the first blank from the top?
hydrogenation
What is the last blank?
halogenation
What is the second blank from the top?
halohydrin formation
What is the third blank from the top?
methyl shift
Why is the minor product (top right) not observed when the reaction is done in the lab?
Halogenation
Without H, adding 2 halogens, break pi bond and puts 1 halogen on either carbon thats double bond; anti addition so added to oppose faces of pi bond; reaction is carried out with a solvent that doesnt react
H3C-PPh3, ether
Wittig reaction reduces ketones or aldehydes to alkene
Anti-Markovnikov Alcohol
X not on most substituted C; minor product
Nucleophiles
a chemical species that donates an electron pair to an electrophile to form a chemical bond in relation to a reaction. All molecules or ions with a free pair of electrons or at least one pi bond
Addition (Anti, Electrophilic, Syn)
a reaction involving an increase in the number of groups attached to the alkene and a decrease in the number of elements of unsaturation
Carbene
a reactive intermediate with a neutral carbon atom having only two bonds and two nonbonding electrons; methylene (:CH₂) is the simplest carbene
-E and symmetric H₂,Pd
achiral product
-Z and asymmetric H₂,Pd
achiral product
-Z and symmetric H₂,Pd
achiral product
-E and asymmetric H₂,Pd
achiral product (H₂,Pd)
requires
acid catalyst H2SO4
anti addition
add substituents to opposite sides of the face
syn addition
add substituents to same sides of the face
1)Hg(OAC)₂, H₂O/THF 2)NaBD₄
add, MN
Hydrohalogenation
adding a hydrohalogen (HCl, HBr, HI) carbocation intermediate markov addition
HBr and ROOR
addition of H and Br (anti-markovnikov)
H3O+ and H2Oor H2SO4 and H2O
addition of H and OH (markovnikov) rearrangements possible
HX
addition of H and X (markovnikov) rearrangements possible
1. Hg(OAC)2 + H2O 2. NaBH4
addition of OH (markovnikov) and H no rearrangements
1. Hg(OAc)2 + ROH 2. NaBH4
addition of RO (markovnikov) and H no rearrangements
Halogenation
addition of br2/cl2
H-Br/ROOR
adds 1 halogen,Antimarkonikov
X2/CCl4
adds 2 of the halogen, antiaddition
BH3, THF/NaOH,H20
adds OH, antimarkonikov
H2SO4/H20
adds OH, markonikov, h shift, Carbocation intermediate
HNO3/H2SO4
adds a para NO2 group
mcpba
adds epoxide ring
HX/CCl4
adds halogen, Markonikov, hydrogen shift, carbocation intermediate
Electrophilic Addition
an addition in which the electrophile (electron-pair acceptor) bonds to one of the double-bonded carbons first, followed by the nucleophile
Anti-Addition
an addition in which two groups add to opposite faces of the double bond (as in addition of Br₂)
Syn Addition
an addition in which two groups add to the same face of the double bond (as in osmium tetroxide dihydroxylation)
Important observations about achiral reactant
an optically active product (i.e., an enantiomerically pure compound or even an enantiomerically enriched compound) can never be produced from achiral starting materials and achiral reagents reacting under achiral conditions.
monomer and a trace of a base
anionic polymerization
X2 + H2O
anti addition of OH (markovnikov) and X and enantiomer
RCO3H + H+ +H2O
anti addition of OH and OH epoxide intermediate and enantiomer
X2
anti addition of X and X and enantiomer
Free Radical Addition (HBr, peroxides) - not HCl or HI
anti-Markovnikov (peroxide effect) free radical formation
hydroboration/oxidation
anti-Markovnikov addition
halogenation
anti-addition stereospecific
hydrohalogenation (HX w/ peroxide)
anti-markovnikov
What kind of a solvent is benzene?
aprotic
Solvent for Pinacol reaction
benzene
Carbocation Stability
benzylic~tertiary > allylic~secondary > primary
Dihydroxylation (OSO4)
breaks the pi bond and adds an OH to each of the carbons; syn addition
PhMgBR/H30+
can create an alcohol from a ketone
Reactive intermediates
carbocation, radical, carbanion
monomer and concentrated acid or BF3 and water
cationic polymerization
1) BH3 * THF or B2H6 2) H2O2, NaOH
cis
Ozonloysis (1. O3, 2. DMS or H202,H2O)
cleaves double bonds molozonide/ ozonide intermediate concerted (add O3) 2nd step can differ (depends if you add DMS or H202, H20)
PCC
create aldehyde from primary alcohol and ketone from secondary alcohol
More than one double bond
diene, triene, polyene, butene, etc
t-buok
elimination to form less substituted alkenes
racemic mixture
enantiomers formed in equal amounts (50/50)
product of adding an alcohol to an alkene
ether
Hygrohalogen#5(with two chiral centers)
first step is regiorandom: 2 enantiomers are formed, The addition of Br- is stereorandom: each enantiomer generates two diastereomers = 2 pairs of racemates. [ As you know, a compound with 2 non-equivalent stereocenters has four stereoisomers; all four are formed. ]
-2 chiral centers in products -Carbocation intermediate
four stereoisomers will be formed as products (E & Z don't matter here)
monomer and heat and ROOR
free radical polymerization
NaNH2 in Nh3
good for deprotanating alkynes and alcohols
Anti-addition mechanisms
halogenation, halohydrin formation
Stereospecific rxns
halogenation, halohydrin formation, dihydroxylation, hydrogenation, hydroboration
Syn-addition mechanisms
hydroboration, dihydoxylation, hydrogenation
Carbonyl
ketone or aldehyde
O3 (-78C) + Me2S
ketones and aldehydes (ozonide intermediates) and dimethyl sulfoxide
KMNO4 + heat + H2O
ketones and carboxylic acids
acid catalyzed hydration (H3O+)
markovnikov H-shift Carbocation intermediate
hydrohalogenation (HX w/ CCl4)
markovnikov H-shift Enantiomers are present since the nucleophile can attack from the top or bottom
Oxymercuration - Reduction (1. Hg(OAc)2, H2O - 2. NaBH4)
markovnikov no H-shift anti-syn
alkoxymercuration - Reduction (1. Hg(OAc)2, ROH - 2. NaBH4)
markovnikov no H-shift anti-syn
Hydrohalogenation of Alkenes, addition of X & OH
markovnikov, anti
Oxymercuration-Reduction, addition of H & OH
markovnikov, anti
Hydration of Alkenes, acid catalyzed, addition of H & OH
markovnikov, no stereoselectivity
Hydrohalogenation, addition of H & X
markovnikov, no stereoselectivity
Oxymercuration/Reduction (1. Hg(OAc)2, H2O, 2. NaBH4)
mercurinium ion intermediate Markovnikov no rearrangements OH goes on more substituted carbon substitution with inversion (H replaces the HgOAc but stereochemistry changes- goes on opposite side) first step is anti-addition
-2 chiral centers in products -E and symmetric Cl₂
meso form (R,S)
-2 chiral centers in products -E and symmetric -no H's on Double Bond Cl₂
meso form (R,S)
-2 chiral centers in products -Z and symmetric peroxyacid
meso form of epoxide
-2 chiral centers in products -Z and symmetric -no H's on Double Bond peroxyacid
meso form of epoxide
-2 chiral centers in products -Z and symmetric -no H's on Double Bond H₂,Pd
meso product (R,S)
Carbocation rearrangement
methyl group moves to carbocation intermediate leading to the halide being attached to the carbon with one hydrogen also attached
Inductive stabilization
more electrons surrounding CH3 to stabilize C+
π radicals are...
more stable, less reactive and longer-lived.
Reactivity w/ double bonds
more substituted dbl bond -> more reactivity (more stable -> more stable intermediate -> more reactivity)
2-bromo-butane
name the product
Halohydrin
needs a polar protic solvent like water; places halogen on least substituted carbon while solvent minus hydrogen on the more substituted carbon (example: h20, cut off a H and only place OH on the more substituted carbon) ; anti addition
Arynes are...
neutral intermediates derived from aromatic rings by removing two substituents (highly reactive)
Nitrenes - structure and reactivity
neutral, electron deficient (6 e-) and highly reactive although they have 4 (rather than 2 in carbenes) non-bonded electrons. Also exist in the singlet and triplet state.
Halogenation of Alkenes, Addition of X & X
no regioselectivity, anti
Catalytic hydrogenation, addition of H &H
no regioselectivity, syn
Syn-dihydroxylation (KMnO4 or OsO4), addition of OH and OH
no regioselectivity, syn
hydrohalogenation
non stereoselective (no facial selectivity) racemic mixture formed when achiral reactant diasteromers formed when chiral reactant
Hydroboration-Oxidation, addition of H & OH
nonmarkovnikov, syn
catalyzed alkene addition
not stereoselective (?)
stereoselective rxn
one in which particular stereoisomer formed in excess over others
racemic mixture(cis-2-butene+Br2)
one that has equal amounts of left- and right-handed enantiomers of a chiral molecule.
oxymercuration -reduction
oxymercuration: anti-addition reduction: not stereoselective some retention, some inversion
Ozonolysis
pi bond breaks to form two double bond oxygens
Electrophile
positively charged or neutral species having vacant orbitals that are attracted to an electron rich centre. It participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile.
rearrangements
possible
-2 chiral centers in products -Two groups added SYN or ANTI
product is affected by reactant stereochemistry
Markovnikov's Rule
provides most substituted alkyl halide
-2 chiral centers in products -E and asymmetric peroxyacid
racemic mix of R,R and S,S
-2 chiral centers in products -E and asymmetric -no H's on Double Bond H₂,Pd
racemic mix of R,R and S,S
-2 chiral centers in products -E and asymmetric -no H's on Double Bond peroxyacid
racemic mix of R,R and S,S
-2 chiral centers in products -E and symmetric peroxyacid
racemic mix of R,R and S,S
-2 chiral centers in products -E and symmetric -no H's on Double Bond H₂,Pd
racemic mix of R,R and S,S
-2 chiral centers in products -E and symmetric -no H's on Double Bond peroxyacid
racemic mix of R,R and S,S
-2 chiral centers in products -Z and asymmetric Cl₂
racemic mix of R,R and S,S
-2 chiral centers in products -Z and asymmetric -no H's on Double Bond Cl₂
racemic mix of R,R and S,S
-2 chiral centers in products -Z and symmetric Br₂, H₂O
racemic mix of R,R and S,S
-2 chiral centers in products -Z and symmetric Cl₂
racemic mix of R,R and S,S
-2 chiral centers in products -Z and symmetric -no H's on Double Bond Cl₂
racemic mix of R,R and S,S
-2 chiral centers in products -Z and asymmetric Br₂,H₂O
racemic mix of R,R and S,S (two pairs of enantiomers=4 products since no regioselectivity)
-2 chiral centers in products -Z and asymmetric -no H's on Double Bond Br₂,H₂O
racemic mix of R,R and S,S (two pairs of enantiomers → 4 products since no regioselectivity)
-2 chiral centers in products -E and asymmetric Cl₂
racemic mix of R,S and S,R
-2 chiral centers in products -E and asymmetric -no H's on Double Bond Cl₂
racemic mix of R,S and S,R
-2 chiral centers in products -E and symmetric Br₂,H₂O
racemic mix of R,S and S,R
-2 chiral centers in products -E and symmetric -no H's on Double Bond Br₂,H₂O
racemic mix of R,S and S,R
-2 chiral centers in products -Z and asymmetric peroxyacid
racemic mix of R,S and S,R
-2 chiral centers in products -Z and asymmetric -no H's on Double Bond H₂,Pd
racemic mix of R,S and S,R
-2 chiral centers in products -Z and asymmetric -no H's on Double Bond peroxyacid
racemic mix of R,S and S,R
-2 chiral centers in products -E and asymmetric Br₂,H₂O
racemic mix of R,S and S,R (two pairs of enantiomers=4 products since no regioselectivity)
-2 chiral centers in products -E and asymmetric -no H's on Double Bond Br₂,H₂O
racemic mix of R,S and S,R (two pairs of enantiomers=4 products since no regioselectivity)
-0 chiral centers in reactant -1 chiral center in products
racemic mixture
Diels-Alder Reaction -1 chiral center in product
racemic mixture -if substituents in dienophile are cis, then they will be cis in products -if substituents in dienophile are trans, then they will be trans in products
NBS, light, low Br2
radical substitution
hydroboration (alkyne)
reactant: (1) BH3 (2) NaOH, H2O2 (terminal) triple bond breaks one bond to H 2 bonds to O (internal) 2 products double bond to O can bond to either end
hydroboration (alkene)
reactant: (1) BH3 (2) NaOH, H2O2 product: anti markovnikov alcohol (least subbed alcohol) less hindered alkene reacts first 1. double bond breaks, one end to H, other end to BH2. 2. BH2 replaced with OH
dihydroxylation (alkene)
reactant: (1) OsO4 (2) NaHSO3 product: syn hydroxides double bond breaks and both ends bond with OH
alkyne preparation
reactant: (1) X2 (2) NaNH2 1. double bond breaks to bond with X on each end 2. strong base breaks bonds in (1) and forms triple bond
oxymercuration (alkene)
reactant: (1) compound with mercury and water (2) NaBH4 product: most subbed alcohol double bond breaks to form with mercury ion intermediate then breaks to form with H and OH
ozonolysis (alkyne)
reactant: (1) ozone (2) Zn, HOAc 1. triple bond splits compound into pieces 2. NaOH & H2O2 oxidize H to OH (terminal alkenes become CO2)
ozonolysis (alkene)
reactant: (1) ozone (2) Zn, HOAc breaks bond into halves at point where double bond occurs forms double bond to oxygen where double bond was broken if OH and H2O2 in reactant, H repalced with OH in products
alkyne alkylation (alkyne)
reactant: (1) strong base (NaNH2, nBuLi, LDA) terminal alkyne deprotonated by base hallide bonds with electron and R group attach bonds with compound
alkene hx addition (alkene)
reactant: HX double bond breaks and one end connects to H, other end connects to X can rearrange
HX addition (alkyne)
reactant: HX product: triple bond breaks to bond with two X and 2 H
hydration: HgSO4, water, H2SO (alkyne)
reactant: HgSO4, water, H2SO triple bond breaks other 2 bonds with O
alkene hydration 1: acid and water (alkene)
reactant: acid (sulfuric or phosphoric) and water product: most subbed alcohol double bond breaks to bond w/ H, other end bonds with OH-
alkene isomerization (alkene)
reactant: acid (sulfuric or phosphorous) most stable (most substituted) carbocation forms lose H and this leads to rearrangement
hydrogenation (alkene)
reactant: diatomic H, Pd/C product: syn addition of H to both sides of double bond
hallide addition (alkene)
reactant: diatomic X product: anti addition of X forms bromium or chloronium intermediate double bond breaks to form with partial positive X (both ends), then breaks to form trans with other X
halide addition (alkyne)
reactant: diatomic X (xs) product: forms 2 bonds with X at both ends of bond
halohydrin formation (alkene)
reactant: diatomic X, water product: anti addition of OH and X intermediate X ion intermediate
what happes to acid catalyst/nuc
regenerated to neutralize the protonated ether
Regiochemistry
regioisomers
Ortho-benzyne radical types
singlet (paired) and triplet (unpaired) diradicals
NBS/NCS
source of Br and Cl
H₃O⁺ Notice that an epoxide formed from an alkene first. Stereo - Anti Addn
steps/reagents involved (Anti Hydroxylation)
HIO₄; H₂O
steps/reagents involved (Cleavage of Two Diols)
CHCl₃, KOH
steps/reagents involved (Dichlorocarbene Addition)
mCPBA, CH₂Cl₂
steps/reagents involved (Epoxation)
X₂ Stereo - Anti Addn Halonium ion intermediate
steps/reagents involved (Halogenation)
X₂; H₂O Regio - OH goes on the more substituted carbon Stereo - Anti
steps/reagents involved (Halohydrin Formation)
1. BH₃, THF 2. H₂O₂, NaOH
steps/reagents involved (Hydroboration)
H₂, Pd/C or PtO₂ Regio - N/A Stereo - Syn Addition
steps/reagents involved (Hydrogenation)
1. O₃ 2. Zn/H₃O⁺
steps/reagents involved (Oxidative Cleavage)
KMnO₄, H₃O⁺
steps/reagents involved (Oxidative Cleavage)
1. Hg(OAc)₂, H₂O/THF 2. NaBH₄
steps/reagents involved (Oxymercuration)
CH₂I₂; Zn(Cu), Ether
steps/reagents involved (Simmons-Smith Reaction)
1. OsO₄ 2. H₂O₂ or NaHSO₃/H₂O
steps/reagents involved (Syn Hydroxylation)
epoxidation
stereospecific syn addition retention
dihydroxylation
stereospecific syn addition achiral reactant forms enantiomers chiral reactant forms diastereomers
Ru or MO
switch groups
hydrohalogenation (H2/pt)
syn addition
CHX3 + NaOH + H2O
syn addition cyclopropination and salt Alpha elimination and enantiomer
H2 + Pt or Pd or Ni
syn addition of H and H
1. BH3 THF 2. H2O2, -OH
syn addition of H and OR (anti-markovnikov) no rearrangements and enantiomer
OsO4 + H2O2
syn addition of OH and OH
KMNO4 (cold dilute) + H2O + -OH
syn addition of OH and OH and enantiomer
epoxidation (ROOH)
syn addition! mCPBA Enantiomers are possible
CH2I2 Zn, CuCl
syn cyclopropination Simmons-Smith, carbenoid intermediate and enantiomer
RCO3H
syn epoxidation and enantiomer
1)BH₃, THF 2)H₂O₂, -OH
syn, anti-MN
Catalytic Hydrogenation (H2, Pd/C)
syn-addition
hydroboration oxidation
syn-addition stereospecific (concerted addition -added at the same time ) enantiomers formed
Hydroboration/ Oxidation (1. BH3*THF, 2. H2O2, OH-)
syn-addition substitution with retention (OH replaces the BR2, on less substituted carbon) concerted no rearrangements anti-Markovnikov
Regioselectivity
the preference of one direction of chemical bond making or breaking over all other possible directions
Demercuration
the removal of a mercury species from a molecule; demercuration of the products of oxymercuration is usually accomplished using sodium borohydride (NaBH₄)
Hyperconjugation
the stabilising interaction that results from the interaction of the electrons in a σ-bond (usually C-H or C-C) with an adjacent empty or partially filled p-orbital or a π-orbital to give an extended molecular orbital that increases the stability of the system.
Carbene
two substituents and one lone pair
-1 nonparticipating, chiral centers in reactant -1 chiral center in products
unequal amounts of diastereomers
Solvent must be...
unreactive to radicals and deoxygenated before reaction